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ap6502a document number: ds35812 rev. 3 - 2 1 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a 240khz 23v 2a synchronous dc/dc buck converter description the ap6502a is a 240khz switchi ng frequency external compensated synchronous dcdc buck converter. it has integrated low r dson high and low side mosfets. the ap6502a enables continues load current of up to 2a with efficiency as high as 95%. the ap6502a features current mode control operation, which enables fast transient response times and easy loop stabilization. the ap6502a simplifies board layout and reduces space requirements with its high level of integration and minimal need for external components, making it ideal for distributed power architectures. the ap6502a is available in a standard green so-8ep package with exposed pad for improved thermal performance and is rohs compliant. features ? v in 4.75v to 23v ? 2a continuous output current, 3a peak ? v out adjustable to 0.925 to 16v ? 240khz switching frequency ? programmable soft-start ? enable pin ? protection ? ocp ? thermal shutdown ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) pin assignments figure 1. package pin out applications ? gaming consoles ? flat screen tv sets and monitors ? set top boxes ? distributed power systems ? home audio ? consumer electronics ? network systems ? fpga, dsp and asic supplies ? green electronics notes: 1. no purposely added lead. fully eu directiv e 2002/95/ec (rohs) & 2011/6 5/eu (rohs 2) compliant. 2. see http://www.diodes.com for more in formation about diodes incorpor ated?s definitions of halogen- and antimony-free, "gree n" and lead-free. 3. halogen- and antimony-free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds . typical applications circuit figure 2. typical application circuit so-8ep (top view) 1 2 3 4 8 7 6 5 ss en comp fb bs in sw gnd 0 0.4 0.8 1.2 1.6 2 load current (a) efficiency vs. load current effi c ien c y ( % ) l = 10h v = 3.3v out 40 50 60 70 80 90 100 v = 5v in v = 12v in
ap6502a document number: ds35812 rev. 3 - 2 2 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a pin descriptions pin number pin name function 1 bs high-side gate drive boost input. bs supplies the dr ive for the high-side n-channel mosfet switch. connect a 0.01f or greater capacitor from sw to bs to power the high side switch. 2 in power input. in supplies the power to the ic, as well as the step-down converter sw itches. drive in with a 4.75v to 23v power source. bypass in to gnd with a su itably large capacitor to eliminate noise on the input to the ic. see input capacitor. 3 sw power switching output. sw is the switching node that supplies power to the output. connect the output lc filter from sw to the output load. note that a capacitor is required from sw to bs to power the high-side switch. 4 gnd ground (connect the exposed pad to pin 4). 5 fb feedback input. fb senses the output voltage and regulat es it. drive fb with a resistive voltage divider connected to it from the output voltage. the feedback th reshold is 0.925v. see setting the output voltage. 6 comp compensation node. comp is used to compensate the regulation control loop. connect a series rc network from comp to gnd. in some cases, an additional capacitor from comp to gnd is required. see compensation components. 7 en enable input. en is a digital input that turns the regula tor on or off. drive en high to turn on the regulator; low to turn it off. attach to in with a 100k ? pull up resistor for automatic startup. 8 ss soft-start control input. ss controls the soft-start period. connect a capacitor from ss to gnd to set the soft- start period. a 0.1f capacitor sets the soft-start peri od to 15ms. to disable the soft-start feature, leave ss floating. ep ep ep exposed thermal pad connect to pin 4 gnd functional block diagram figure 3. functional block diagram
ap6502a document number: ds35812 rev. 3 - 2 3 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a absolute maximum ratings (note 4) (@t a = +25c, unless otherwise specified.) symbol parameter rating unit v in supply voltage -0.3 to +26 v v sw switch node voltage -1.0 to v in +0.3 v v bs bootstrap voltage v sw -0.3 to v sw +6 v v fb feedback voltage -0.3v to +6 v v en enable/uvlo voltage -0.3v to +6 v v comp comp voltage -0.3v to +6 v t st storage temperature -65 to +150 c t j junction temperature +150 c t l lead temperature +260 c esd susceptibility (note 5) hbm human body model 3 kv mm machine model 250 v notes: 4. stresses greater than the 'absolute maximum ratings' specified above may cause permanent damage to the device. these are stress ratings only; functional operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. device reliability may be affected by exposure to absolute ma ximum rating conditions for extended periods of time. 5. semiconductor devices are esd sensitive and may be damaged by exposure to esd events. suitable esd precautions should be taken when handling and transporting these devices. thermal resistance (note 6) symbol parameter rating unit ja junction to ambient so-8ep 74 c/w jc junction to case so-8ep 16 note: 6. test condition: so-8ep: device mounted on 1" x 1" fr -4 substrate pc board, 2oz copper, with minimum recommended pad on top layer and thermal vias to bottom layer ground plane. recommended operating conditions (note 7) (@t a = +25c, unless otherwise specified.) symbol parameter min max unit v in supply voltage 4.75 23 v t a operating ambient temperature range -40 +85 c note: 7. the device function is not guaranteed outside of the recommended operating conditions.
ap6502a document number: ds35812 rev. 3 - 2 4 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a electrical characteristics (v in = 12v, @t a = +25c, unless otherwise specified.) symbol parameter test conditions min typ max unit i in shutdown supply current v en = 0v 0.3 3.0 a i in supply current (quiescent) v en = 2.0v, v fb = 1.0v 0.6 1.5 ma r ds(on)1 high-side switch on-resistance (note 8) 130 m ? r ds(on)2 low-side switch on-resistance (note 8) 130 m ? i limit hs current limit minimum duty cycle 4.4 a i limit ls current limit from drain to source 0.9 a high-side switch leakage current v en = 0v, v sw = 0v, v sw = 12v 0 10 a avea error amplifier voltage gain (note 8) 800 v/v gea error amplifier transconductance i c = 10a 1000 a/v gcs comp to current sense transconductance 2.8 a/v f sw oscillator frequency v fb = 0.75v 210 240 260 khz f fb fold-back frequency v fb = 0v 0.30 f sw d max maximum duty cycle v fb = 800mv 90 % t on minimum on time 130 ns v fb feedback voltage t a = -40c to +85c 900 925 950 mv feedback overvoltage threshold 1.1 v v en_rising en rising threshold 0.7 0.8 0.9 v en lockout threshold voltage 2.2 2.5 2.7 v en lockout hysteresis 220 mv inuv vth v in under voltage threshold rising 3.80 4.05 4.40 v inuv hys v in under voltage threshold hysteresis 250 mv soft-start current v ss = 0v 6 a soft-start period c ss = 0.1f 15 ms t sd thermal shutdown (note 6) 160 c note: 8. guaranteed by design.
ap6502a document number: ds35812 rev. 3 - 2 5 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a typical performance graphs (v in = 12v, v out = 3.3v, t a = +25c, unless otherwise specified.) quiescent supply current (ma) 0.48 0.5 0.52 0.54 0.56 0.58 0.6 0 5 10 15 20 input voltage (v) quiescent supply current vs. input voltage shutdown supply current (a) 0 5 10 15 20 input voltage (v) shutdown supply current vs. input voltage 0.004 0.014 0.024 0.034 0.044 0.054 0.064 0.074 current limit (a) 4.8 5 5.2 5.4 5.6 5.8 6 6.2 -60 -40 -20 0 20 40 60 80 100 temperature (c) current limit vs. temperature output voltage (v) v = 12v in 3.32 3.321 3.322 3.323 3.324 3.325 3.326 3.327 3.328 3.329 3.33 41 01 52 0 input voltage (v) line regulation -60 -40 -20 0 20 40 60 80 100 temperature (c) feedback voltage vs. temperature feedba c k v o l t a g e (v) 0.9 0.902 0.904 0.906 0.908 0.91 0.912 0.914 0.916 0.918 0.92 225 230 235 240 245 250 25 5 -60 -40 -20 0 20 40 60 80 100 temperature (c) oscillator frequency vs. temperature oscillator frequency (khz)
ap6502a document number: ds35812 rev. 3 - 2 6 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a typical performance characteristics (v in = 12v, v out = 3.3v, l = 3.3h, c1 = 22f, c2 = 47f, t a = +25c, unless otherwise specified.) steady state test no load time -2s/div steady state test 2 a time -2s/div startup through enable_no load time -10ms/div startup through enable 2 a time -2ms/div shutdown through enable_no load time -10ms/div shutdown through enable 2 a time -5ms/div load transient test 1.0a to 2.0 a time -100s/div short circuit test time -20s/div short circuit recovery time -50s/div
ap6502a document number: ds35812 rev. 3 - 2 7 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a application information theory of operation the ap6502a is a 2a current mode control, synchronous buck regulator with built in power mosfets. current mode control assures excellent line and load regulation and a wide loop bandwidth fo r fast response to load transients. figure 3 depicts the functional block diagram of ap6502a. the operation of one switching cycle can be explained as follows. at the beginning of each cycle, hs (high-side) mosfet is off. the error amplifier (ea) output voltage is higher than the current sense amplifier output, and the current comparator?s output is low. the rising edge of the 240khz oscillator clock signal sets the rs flip-flop. its output turns on hs mosfet. the current sense amplifier is reset for e very switching cycle. when the hs mosfet is on, inductor current starts to increase. the current sense am plifier senses and amplifies the inductor cu rrent. since the current mode control is subject to sub-harmonic oscillations that peak at half the switching frequency, ramp slope compensa tion is utilized. this will help to stabilize the power supply. this ramp compens ation is summed to the current sense amplifier output and compar ed to the error amplifier output by the pwm comparator. when the sum of the cu rrent sense amplifier output and the slope compensation signal ex ceeds the ea output voltage, the rs flip-flop is reset and hs mosfet is turned off. for one whole cycle, if the sum of the current sense amplif ier output and the slope compensation signal does not exceed the ea output, then the falling edge of the oscillator clock resets the flip-flop. the output of the error amplifier increases when feedback voltage (v fb ) is lower than the reference voltage of 0.925v. this also increases the i nductor current as it is proportional to the ea voltage. if in one cycle the current in the power mosfet does not reach th e comp set current value, the power mosfet will be forced to turn off. when the hs mosfet turns off, the synchronous ls mosfet turns on unt il the next clock cycle begins. there is a ?dead time? between the hs turn off and ls turn on that prevents the switches from ?shooting through? from the input supply to ground. the voltage loop is compensated through an internal transconduct ance amplifier and can be adjusted through the external compens ation components. enable above the ?en rising threshold?, the inter nal regulator is turned on and the quiescent current can be measured above this thres hold. the enable (en) input allows the user to control turning on or off t he regulator. to enable the ap6502a, en must be pulled above the ?en l ockout threshold voltage? and to disable the ap6502a, en must be pulled below ?en lo ckout threshold voltage - en lockout hysteresis? (2.2v - 0.2 2v = 1.98v). external soft start soft start is traditionally implemented to prevent the excess inru sh current. this in turn prevents the converter output voltage from overshooting when it reaches regulation. the ap6502a has an internal current source with a soft start capacitor to ramp the reference voltage from 0v to 0.925v. the soft start current is 6a. the soft start sequence is reset when there is a thermal shutdown, under voltage lockout (uvlo) or when the part is disabled using the en pin. external soft start can be calculated from the formula below: dt dv *c ss i = where; i ss = soft start current c = external capacitor dv = change in feedback voltage from 0v to maximum voltage dt = soft start time current limit protection in order to reduce the total power dissipation and to protect the application, ap6502a has cycle-by-cycle current limiting impl ementation. the voltage drop across the internal high-side mosfet is sensed and compared with the internally set current limit threshold. this voltage drop is sensed at about 30ns after the hs turns on. when the peak inducto r current exceeds the set current limit threshold, current lim it protection is activated. during this time the feedback voltage (v fb ) drops down. when the voltage at the fb pin r eaches 0.3v, the internal oscillator shifts the frequency from the normal operating frequency of 240khz to a fold- back frequency of 80khz. the current limit is reduced to 70% of nominal current limit when the part is operating at 80khz. th is low fold-back frequency prevents runaway current.
ap6502a document number: ds35812 rev. 3 - 2 8 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a application information (cont.) under voltage lockout (uvlo) under voltage lockout is implemented to prevent the ic from insufficient input voltages. the ap6502a has a uvlo comparator that monitors the input voltage and the internal bandgap reference. if the input voltage falls below 4.0v, the ap6502a will latch an under vo ltage fault. in this event the output will be pulled low and power has to be re-cycled to reset the uvlo fault. over voltage protection when the ap6502a fb pin exceeds 20% of the nominal regulation voltage of 0.925v, the over voltage comparator is tripped and the comp pin and the ss pin are discharged to gnd, forcing the high-side switch off. thermal shutdown the ap6502a has on-chip thermal protection that prevents damage to the ic when the die temperature exceeds safe margins. it imp lements a thermal sensing to monitor the operating j unction temperature of the ic. once the die temperature rises to approximately +160c , the thermal protection feature gets activated. the inter nal thermal sense circuitry turns the ic of f thus preventing the power switch from damage. a hysteresis in the thermal sense circuit allows the device to cool down to approximately +120c before the ic is enabled again through soft start. this thermal hysteresis feature prevents undesir able oscillations of the t hermal protection circuit. setting the output voltage the output voltage can be adjusted from 0.925v to 16v using an external resistor divider. table 1 shows a list of resistor selection for common output voltages. resistor r1 is selected based on a design tr adeoff between efficiency and output voltage accuracy. for high va lues of r1 there is less current consumption in the feedback network. however the trade off is output voltage accuracy due to the bias current i n the error amplifier. r1 can be determined by the following equation: ? ? ? ? ? ? ? ? ??= 1 0.925 out v 2 r 1 r figure 4 feedback divider network when output voltage is low, network as shown in figure 4 is recommended. v out (v) r1 (k ? ) r2 (k ? ) 5 45.3 10 3.3 26.1 10 2.5 16.9 10 1.8 9.53 10 1.2 3 10 table 1. resistor selection for common output voltages compensation components the ap6502a has an external comp pin through which system stabilit y and transient response can be c ontrolled. comp pin is the o utput of the internal trans-conductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. the dc gain of the voltage feedback loop is given by: out fb vea cs load vdc v v agra =
ap6502a document number: ds35812 rev. 3 - 2 9 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a application information (cont.) compensation components (cont.) where v fb is the feedback voltage (0.925v), r load is the load resistor value, g cs is the current sens e trans-conductance and a vea is the error amplifier voltage gain. the control loop transfer function incorpor ates two poles one is due to the compensat ion capacitor (c3) and the output resistor of error amplifier, and the other is due to the output capacitor and th e load resistor. these poles are located at: vea ea p1 a3c2 g f = load p2 r2c2 1 f = where g ea is the error amplifier trans-conductance. one zero is present due to the compensation capacitor (c3) an d the compensation resistor (r3). this zero is located at: 3r3c2 1 f z1 = the goal of compensation design is to shape the converter transfer function to get a desired loop gain. the system crossover fr equency where the feedback loop has the unity gain is crucial. a rule of thumb is to set the crossover frequency to below one-tenth of the switching frequency. use the following procedure to optimize the compensation components: 1. choose the compensation resistor (r3) to set the desired cr ossover frequency. determine the r3 value by the following equati on: fb out cs g ea fb out csea v v g fs1.02c2 v v gg fc2c2 3r < = where f c is the crossover frequency, which is typically less than one tenth of the switching frequency. 2. choose the compensation capacitor (c3) to achieve the desired phase ma rgin set the compensation zero, f z1 , to below one fourth of the crossover frequency to provide sufficient phase margin. determine the c3 value by the following equation: fc3r 2 3c > where r3 is the compensation resistor value. v out (v) c in /c1 (f) c out /c2 (f) r c /r3 (k ? ) c c /c3 (nf) l1 (h) 1.2 22 47 3.24 6.8 3.3 1.8 22 47 6.8 6.8 3.3 2.5 22 47 6.8 6.8 10 3.3 22 47 6.8 6.8 10 5 22 47 6.8 6.8 10 12 22 47 6.8 6.8 15 table 2. recommended component selection
ap6502a document number: ds35812 rev. 3 - 2 10 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a application information (cont.) inductor calculating the inductor value is a critic al factor in designing a buck converter. for most designs, the following equation can be used to calculate the inductor value; sw f l i in v ) out v in (v out v l ?? ?? = where l i is the inductor ripple current. and sw f is the buck converter switching frequency. choose the inductor ripple current to be 30% of the maximum load current. the maximum inductor peak current is calculated from: 2 l i load i l(max) i += peak current determines the required saturation current rating, which influences the size of the inductor. saturating the inductor decreases the converter efficiency while increasing the te mperatures of the inductor and the internal mosfets. hence choosing an inductor wit h appropriate saturation current rating is important. a 1h to 10h inductor with a dc current rating of at least 25 % percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor ?s dc resistance should be less than 200m ? . use a larger inductance for im proved efficiency under light load conditions. input capacitor the input capacitor reduces the surge current drawn from the i nput supply and the switching noise from the device. the input ca pacitor has to sustain the ripple current produced during the on time on the upp er mosfet. it must hence have a low esr to minimize the losses . the rms current rating of the input capacitor is a critical parameter that must be hi gher than the rms input current. as a rule of thumb, select an input capacitor which has rms rating that is greater than half of the maximum load current. due to large di/dt through the input capacitors, electrolytic or ceramics should be used. if a tantalum must be used, it must b e surge protected. otherwise, capacitor failure could occur. for most applications, a 4.7f cerami c capacitor is sufficient. output capacitor the output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the ou tput voltage. the output capacitor is a basic component for th e fast response of the power supply. in fact, during load trans ient, for the first few microseconds it supplies the current to the load. the converter recognizes the load transient and sets the duty cycle to maximum, but the curre nt slope is limited by the inductor value. maximum capacitance required can be calc ulated from the following equation: esr of the output capacitor dominates the output voltage ripple. the amount of ripple can be ca lculated from the equation below : esr* inductor i capacitor vout = an output capacitor with ample capacitance and low esr is the bes t option. for most applications , a 22f ceramic capacitor will be sufficient. 2 out 2 out 2 inductor out o v)v v( ) 2 i l(i c ?+ + = where v is the maximum output voltage overshoot.
ap6502a document number: ds35812 rev. 3 - 2 11 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a application information (cont.) pc board layout this is a high switching frequency converter. hence attention mu st be paid to the switching currents interference in the layout . switching current from one power device to another can generate voltage transient s across the impedances of the interconnecting bond wires and ci rcuit traces. these interconnecting impedances shoul d be minimized by using wide, sh ort printed circuit traces. AP6502ASP-13 is exposed at the bottom of the package and must be soldered directly to a well designed thermal pad on the pcb. t his will help to increase the power dissipation. external bootstrap diode it is recommended that an external bootstrap diode be added when the input voltage is no greater than 5v or the 5v rail is avai lable in the system. this helps to improve the efficiency of the regulator. this solution is also applicable for d > 65%. the bootstrap diod e can be a low cost one such as bat54 or a schottky that has a low vf. figure 7. external bootstrap compensation components recommended diodes: part number voltage/current rating vendor b130 30v, 1a diodes inc sk13 30v, 1a diodes inc
ap6502a document number: ds35812 rev. 3 - 2 12 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a ordering information part number package code packaging 13? tape and reel quantity part number suffix AP6502ASP-13 sp so-8ep 2500/tape & reel -13 marking information package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. ? ap6502a - x x13 packing package sp : so-8ep 13 : tape & reel so-8ep (sop-8l-ep) dim min max typ a 1.40 1.50 1.45 a1 0.00 0.13 - b 0.30 0.50 0.40 c 0.15 0.25 0.20 d 4.85 4.95 4.90 e 3.80 3.90 3.85 e0 3.85 3.95 3.90 e1 5.90 6.10 6.00 e - - 1.27 f 2.75 3.35 3.05 h 2.11 2.71 2.41 l 0.62 0.82 0.72 n - - 0.35 q 0.60 0.70 0.65 all dimensions in mm gauge plane seating plane e1 e n e b a 45 e0 h f exposed pad bottom view l q c 7 4 3 9 (all sides) a1 d 14 85
ap6502a document number: ds35812 rev. 3 - 2 13 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a suggested pad layout please see ap02001 at http://www.diodes.com/dat asheets/ap02001.pdf for the latest version. dimensions value (in mm) c 1.270 x 0.802 x1 3.502 x2 4.612 y 1.505 y1 2.613 y2 6.500 c y1 x1 x y y2 x2
ap6502a document number: ds35812 rev. 3 - 2 14 of 14 www.diodes.com december 2012 ? diodes incorporated new product a p6502a important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product descri bed herein. diodes incorporated does not assume any liability arising out of the application or use of this document or an y product described herein; neither does di odes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or us er of this document or products described herein in such applica tions shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes inco rporated products for any unintended or una uthorized application, customers shall i ndemnify and hold diodes incorporated and its representativ es harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death a ssociated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. this document is written in english but may be translated into multiple languages for reference. only the english version of t his document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical component s in life support devices or systems without the express written approval of the chief executive offi cer of diodes incorporated. as used herein: a. life support devices or syst ems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when proper ly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support devic e or system whose failure to perform can be reasonably expect ed to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifi cations of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-rel ated requirements concerning the ir products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or s ystems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporate d and its representatives against any damages arisi ng out of the use of diodes incorporated pr oducts in such safety-critical, life suppor t devices or systems. copyright ? 2012, diodes incorporated www.diodes.com

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